The present invention relates to a constant velocity universal joint for use in power transmission devices in motor vehicles and various industrial machines. In particular, the invention relates to a tripod type constant velocity universal joint.
Tripod type constant velocity universal joints are used, for example, as an element in a power transmission device for transmitting rotational power from a car engine to wheels (as a joint for coupling drive shafts or propeller shafts).
In general, a tripod type constant velocity universal joint is chiefly composed of an outer joint member and a tripod member. The outer joint member has an inner periphery provided with three track grooves, each of which has axial roller guideways on both sides. The tripod member has three radially-projecting trunnions. A roller is rotatably arranged on each of the trunnions. The trunnions of the tripod member and the roller guideways in the outer joint member engage with each other in the direction of rotation via the rollers so that rotational torque is transmitted from a drive side to a driven side at constant velocity. The individual rollers rotate about the trunnions and roll on the roller guideways as well, absorbing relative axial displacements and angular displacements between the outer joint member and the tripod member. In the meantime, also absorbed are axial displacements of the individual trunnions to the roller guideways, the axial displacements resulting from phase changes in the direction of rotation when the outer joint member and the tripod member transmit rotational torque with some operating angle therebetween.
Among factors contributing to the vibration characteristics of a constant velocity universal joint of this type are induced thrust and slide resistance. The induced thrust is a periodic varying force produced by friction between internal parts of the constant velocity universal joint when the joint transmits rotational torque with an operating angle. That is, due to the rotational motion, the individual trunnions of the tripod member and the rollers inevitably repeat relative axial reciprocation to the roller guideways. In that case, friction occurs at such portions as between the rollers and the roller guideways, and between the rollers and the trunnions. This friction produces the induced thrust. Thus, the induced thrust is a varying force inherent in a constant velocity universal joint, inevitably occurring in relation to the internal structure and rotational motion of the joint. In the case of a tripod type constant velocity universal joint, the induced thrust consists chiefly of a variation component of third order (tertiary rotational component) because the numbers of trunnions and rollers are three. Meanwhile, the slide resistance is a periodic varying force produced by friction between the internal parts when external vibrations are input to the constant velocity universal joint under torque. In other words, the slide resistance indicates the vibration transfer characteristics of the constant velocity universal joint.
For the power transmission device of a motor vehicle, the vibrations resulting from the induced thrust and slide resistance of the constant velocity universal joint are rather small in level as compared with engine vibrations and the like, and thus matter little by themselves. Nevertheless, the vibrations, if approaching the engine vibrations and the like in frequency, cause resonance phenomena. The induced thrust causes the rolling of a car body at starts and under acceleration, as well as muffled noise, beat noise, and so on. The slide resistance causes an increase of idling vibrations and the like (in particular, affecting the Drive or D-range idling vibrations). Accordingly, the induced thrust and slide resistance in the constant velocity universal joint have significant influence on the NVH (noise vibration harshness) performances of the motor vehicle. In particular, the induced thrust is ever increasing in the degree of influence on the NVH performances, with widening regular-use angles (vehicle-mounted angles) of the joint and increasing torque in recent times. Then, in terms of vehicle design, it means that the values of the induced thrust and slide resistance of constant velocity universal joints constitute greater constraints on the layout design of power transmission systems.